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32 lines
1.0 KiB
Go
32 lines
1.0 KiB
Go
//go:build !js && !ios && !android
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package server
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import "unsafe"
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// swizzleBGRAtoRGBA swaps B and R channels in a BGRA pixel buffer and copies
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// into dst in-place (dst and src may alias). Operates on uint32 words: one
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// read-modify-write per pixel, which is meaningfully faster than the naive
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// three-byte-store per pixel for large buffers like framebuffers.
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//
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// The alpha byte is forced to 0xff so callers that capture from X11 GetImage
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// (where the X server leaves the pad byte as zero) still get an opaque image.
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func swizzleBGRAtoRGBA(dst, src []byte) {
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n := len(dst) / 4
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if len(src)/4 < n {
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n = len(src) / 4
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}
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if n == 0 {
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return
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}
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dp := unsafe.Slice((*uint32)(unsafe.Pointer(&dst[0])), n)
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sp := unsafe.Slice((*uint32)(unsafe.Pointer(&src[0])), n)
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for i := range n {
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p := sp[i]
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// p in memory: B, G, R, A -> as uint32 little-endian: 0xAARRGGBB
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// Want memory: R, G, B, 0xFF -> uint32 little-endian: 0xFFBBGGRR
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dp[i] = 0xFF000000 | (p & 0x0000FF00) | ((p & 0x00FF0000) >> 16) | ((p & 0x000000FF) << 16)
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}
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}
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